The balsam twig aphid feeds on the new growth of fir causing distorted needles and deposits of honeydew. Trees can tolerate fairly heavy infestations for a short period of time but are weakened by repeated heavy infestations. Sprays of Orthene or malathion may be used according to the label directions for aphids on fir.
Bagworm builds, and lives in, a two to three inch long sack built from needles. The insect overwinters as an egg in the sacks of the females. Control by hand-picking the bags in winter. Sprays are formulations of Bacillus thuringiensis, Diazinon, or malathion.
The more common scale insects infesting fir are oystershell, pine needle, and cottony cushion. These insects are hard to control once inside their shell or waxy coatings. The crawler stage may be controlled with sprays of Orthene, or malathion.
Spider mites cause older needles to lose green coloration and become yellowed. The insects are very small and difficult to see so infestations can become severe before being noticed. Mites may be controlled with sprays of Orthene. Dormant sprays of superior oil may also be used.
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